Conventionally, there is disclosed a cylinder block plate processing apparatus for sealing one end side (crankcase surface side) of an inner peripheral surface of a cylinder of a cylinder block to circulate a process liquid, and performs pre-plate processing or plate processing of the cylinder inner peripheral surface (for example, Japanese Patent Laid-Open Publication No. 8-74095: Patent Document 1). This conventional example describes an apparatus in which a balloon-shaped sealing member is inserted from a crankcase surface side into a cylinder, and the sealing member seals the crankcase surface side of a cylinder inner peripheral surface.
However, in recent engines, pitches of a plurality of cylinders tend to be reduced in term of a demand for a size reduction. In a cylinder block of such an engine, a crank journal that journals a crankshaft with a crankcase is formed to overhang inward of the cylinder on a crankcase surface side.
When plate processing to such a cylinder block is performed, if a sealing member is to be inserted from the crankcase surface side, the sealing member interferes with the crank journal, and thus, a shape thereof is significantly limited and becomes complex.
When the sealing member is inserted from the crankcase surface side into the cylinder so as to avoid the crank journal so as to seal thereafter the entire cylinder inner peripheral surface, an amount or rate of size change in expansion/contraction of the sealing member becomes excessive, and then, the sealing accuracy of the sealing member is reduced, and the cylinder inner peripheral surface cannot be reliably sealed.